In the manufacture of integrated circuit devices, photoresists are used as an intermediate mask for transferring the original mask pattern of a reticle onto the wafer substrate by means of a series of photolithography and plasma etching steps. One of the essential steps in the integrated circuit device manufacturing process is the removal of the patterned photoresist films from the wafer substrate. In general, this step is carried out by one of two methods.
One method involves a wet stripping step in which the photoresist-covered substrate is brought into contact with a photoresist stripper solution that consists primarily of an organic solvent and an amine. However, stripper solutions cannot completely and reliably remove the photoresist films, especially if the photoresist films have been exposed to UV radiation and plasma treatments during fabrication. Some photoresist films become highly crosslinked by such treatments and are more difficult to dissolve in the stripper solution. In addition, the chemicals used in these conventional wet-stripping methods are sometimes ineffective for removing inorganic or organometallic residual materials formed during the plasma etching of metal or oxide layers with halogen-containing gases.
An alternative method of removing a photoresist film involves exposing a photoresist-coated wafer to oxygen-based plasma in order to burn the resist film from the substrate in a process known as plasma ashing. However, plasma ashing is also not fully effective in removing the plasma etching by-products noted above. Instead, removal of these plasma etch by-products is typically accomplished by subsequently exposing the processed metal and dielectric thin films to certain cleaning solutions.
Metal substrates are generally susceptible to corrosion. For example, substrates such as aluminum, copper, aluminum-copper alloy, tungsten nitride, tungsten (W), cobalt (Co), titanium oxide, other metals and metal nitrides, will readily corrode and dielectrics [ILD, ULK] can etch by using conventional cleaning chemistries. In addition the amount of corrosion tolerated by the integrated circuit device manufacturers is getting smaller and smaller as the device geometries shrink.
At the same time as residues become harder to remove and corrosion must be controlled to ever lower levels, cleaning solutions must be safe to use and environmentally friendly.
Therefore, the cleaning solution should be effective for removing the plasma etch and plasma ash residues and must also be non-corrosive to all exposed substrate materials.